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174 FILLING MATERIALS

toward the matrix and the other toward the axial wall. (2)
Place the cylinders in position, and condense with wedge-
shaped, serrated hand pluggers, wedging the middle one in
between the other two (Fig. 189). (3) Place in more

cylinders, and continue thus until the filling is nearly on a
level with the top of the step (Fig. 190). (4) Fill the balance
of the cavity as if it were a simple cavity, laying the cylinders
in the opposite direction to that used in filling the first portion
of the cavity, viz., with one end lying on the step and on that
portion of the filling already condensed, and the other end

pointing toward the end of the handle (Fig. 191).
4. Burnish and polish all of the fillings.

GOLD

Characteristics.—Gold, for filling cavities, should be pure.
In its pure state, uncontaminated, it is cohesive. By cohe-
siveness is meant the property which causes separate parti-
cles, when brought in contact, to cling to one another. Gold
possesses this property to a higher degree than any other
metal. It is taken advantage of in building fillings, by weld-

ing the various pieces together in the cold state, by means of
the plugger. Gold and tin are the only metals possessing
to any degree this property of cohesiveness or weldability
in the cold state.

Classification.—Gold, for filling purposes, is classified into
two varieties, as far as its minute or microscopic structure is
concerned.
1. Fibrous gold.
2. Crystalline gold.
If these two forms be examined under the microscope,

the fibrous forms are seen to consist of numerous fibers inter-
lacing each other in every direction; while the crystalline